This invention relates to printed circuit boards, and more particularly to structures that can be used on printed circuit boards (“PCBs”) to facilitate the provision of electrical switches on such boards.
PCBs are frequently constructed so that they can include one or more manually operable electrical switches. An example of such a switch is a so-called dome switch. A dome switch typically includes a circular metal disc that is resiliently biased to form a small dome above a surface of the PCB. The circular outer edge of the disc bears on a ring-shaped outer contact on the surface of the PCB. Another contact (the inner contact) is inside the outer contact on the PCB surface and under the center of (but not normally in contact with) the above-mentioned metal disc. The inner contact is spaced from all parts of the outer contact. The inner contact is therefore not normally in electrical contact with the outer contact. However, the center of the above-mentioned dome can be manually pressed down into contact with the inner contact, thereby forming an electrical connection between the inner and outer contacts and electrically “closing” the switch. When the manual pressure on the dome is released, the metal disc resiliently returns to its “relaxed” dome shape. This moves the center of the dome out of contact with the inner contact and electrically “opens” the switch.
Switches with a moving part or parts (e.g., dome switches) unavoidably subject PCB contacts like those mentioned above to abrasion each time the switch is operated. Some switches (like dome switches) may also need to be “vented” for proper operation. This exposes the PCB contacts to the possibility of corrosion.
To give switches adequate service life, it is typically necessary to plate the PCB contacts with so-called “hard gold.” Hard gold is an alloy of gold and nickel and/or cobalt. Hard gold plating can be expensive and/or difficult when an entire PCB must be subjected to such processing.